1. Field of the Invention
The invention relates in general to methods of performing thermodynamic cycles for generating mechanical and/or electrical power, for heating, and/or cooling.
2. Description of Related Art
Due to customer demand variations, there is a need for gas turbine (GT) power cycles that can operate efficiently at less than full power load (i.e., at or on “part load”). A power producer is often required to reduce their GT output power and reduce fuel use because of insufficient demand for power at various times during the day, week, and year (“off-peak”). However, many existing gas turbine cycles, especially “Brayton” cycles, (including “simple”, Dry-Lo NOX (DLN), and Dry Low Emissions (DLE) cycles), are limited in their ability to operate at reduced power or reduced fuel consumption. E.g., because of compressor stall limits, less efficient combustion with reduced turbine inlet temperature (TIT), and changes in combustion stoichiometry that occur during part load operation. System shutdowns have even been caused by variations in relative humidity and/or pipeline fuel composition. Declining fuel to air ratios when lowering power results in lower turbine inlet temperature and consequently substantially lower efficiency. Conventional water cooling of combustion requires substantial makeup water. A new power cycle with improved control methods is required to address these problems without the drawbacks of the prior art cycles.
In other documents, (e.g. U.S. Pat. No. 5,617,719, U.S. Pat. No. 5,743,080, U.S. Pat. No. 5,289,666, and U.S. patent application Ser. No. 11/149,959) efficient operation of gas turbines with VAST power cycles has been described with high water and/or steam to fuel ratios (typically 5:1-10:1 water:fuel by mass or higher) with high efficiency, high power output and lowered pollutant emission levels as compared to dry cycles. VAST cycles enable recovering exhaust heat into high levels of steam and heated water and recycling this heat into the combustion chamber. Heating water enables recovering and using heat at lower temperatures than with steam alone. Controlling distribution of high water+steam injection levels, enable improved axial and transverse combustion and temperature control, resulting in lower emissions, and higher specific power generation with VAST cycles. High water diluent levels provide greater cooling and control, allowing higher fuel injection rates without component thermal failure. VAST cycles enable net water recovery clean water sales. High water and steam injection levels enables greater overall flexibility for part load applications as will be described in detail below.